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 #include &lt;QtGui&gt;

 #include &quot;arrow.h&quot;
 #include &lt;math.h&gt;

 const qreal Pi = 3.14;

 Arrow::Arrow(DiagramItem *startItem, DiagramItem *endItem,
          QGraphicsItem *parent, QGraphicsScene *scene)
     : QGraphicsLineItem(parent, scene)
 {
     myStartItem = startItem;
     myEndItem = endItem;
     setFlag(QGraphicsItem::ItemIsSelectable, true);
     myColor = Qt::black;
     setPen(QPen(myColor, 2, Qt::SolidLine, Qt::RoundCap, Qt::RoundJoin));
 }

 QRectF Arrow::boundingRect() const
 {
     qreal extra = (pen().width() + 20) / 2.0;

     return QRectF(line().p1(), QSizeF(line().p2().x() - line().p1().x(),
                                       line().p2().y() - line().p1().y()))
         .normalized()
         .adjusted(-extra, -extra, extra, extra);
 }

 QPainterPath Arrow::shape() const
 {
     QPainterPath path = QGraphicsLineItem::shape();
     path.addPolygon(arrowHead);
     return path;
 }

 void Arrow::updatePosition()
 {
     QLineF line(mapFromItem(myStartItem, 0, 0), mapFromItem(myEndItem, 0, 0));
     setLine(line);
 }

 void Arrow::paint(QPainter *painter, const QStyleOptionGraphicsItem *,
           QWidget *)
 {
     if (myStartItem-&gt;collidesWithItem(myEndItem))
         return;

     QPen myPen = pen();
     myPen.setColor(myColor);
     qreal arrowSize = 20;
     painter-&gt;setPen(myPen);
     painter-&gt;setBrush(myColor);

     QLineF centerLine(myStartItem-&gt;pos(), myEndItem-&gt;pos());
     QPolygonF endPolygon = myEndItem-&gt;polygon();
     QPointF p1 = endPolygon.first() + myEndItem-&gt;pos();
     QPointF p2;
     QPointF intersectPoint;
     QLineF polyLine;
     for (int i = 1; i &lt; endPolygon.count(); ++i) {
     p2 = endPolygon.at(i) + myEndItem-&gt;pos();
     polyLine = QLineF(p1, p2);
     QLineF::IntersectType intersectType =
         polyLine.intersect(centerLine, &amp;intersectPoint);
     if (intersectType == QLineF::BoundedIntersection)
         break;
         p1 = p2;
     }

     setLine(QLineF(intersectPoint, myStartItem-&gt;pos()));

     double angle = ::acos(line().dx() / line().length());
     if (line().dy() &gt;= 0)
         angle = (Pi * 2) - angle;

         QPointF arrowP1 = line().p1() + QPointF(sin(angle + Pi / 3) * arrowSize,
                                         cos(angle + Pi / 3) * arrowSize);
         QPointF arrowP2 = line().p1() + QPointF(sin(angle + Pi - Pi / 3) * arrowSize,
                                         cos(angle + Pi - Pi / 3) * arrowSize);

         arrowHead.clear();
         arrowHead &lt;&lt; line().p1() &lt;&lt; arrowP1 &lt;&lt; arrowP2;
         painter-&gt;drawLine(line());
         painter-&gt;drawPolygon(arrowHead);
         if (isSelected()) {
             painter-&gt;setPen(QPen(myColor, 1, Qt::DashLine));
         QLineF myLine = line();
         myLine.translate(0, 4.0);
         painter-&gt;drawLine(myLine);
         myLine.translate(0,-8.0);
         painter-&gt;drawLine(myLine);
     }
 }</pre>
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